Gaseous discharge display device with embedded electrode segments

ABSTRACT

A gas discharge display device for displaying one of a plurality of alpha-numeric characters, including a substrate having a glass layer upon its upper surface; a plurality of flat metal segment elements embedded in the glass layer and arranged laterally in the general shape of the necessary segments of all the alphanumeric characters to be displayed by the device; a plurality of metal leads, one for each segment, each electrically connected to its respective segment and extending outside the periphery of the substrate; a second metal layer electrically insulated from the segments lying in a plane parallel to that of the segments and having apertures therein arranged laterally in correspondence with the segments, the second metal layer being mechanically supported by the substrate; a metal lead electrically connected to the second metal layer also extending outside the periphery of the substrate; and a cover, at least partially translucent, so that the segments, when energized, are visible therethrough, the cover enclosing and sealing the segments and the second metal layer, thereby providing a sealed enclosure with the necessary electrical leads from the cathode segments and the anode extending outside the sealed enclosure so that, when the cathode segments are selectively electrically activated, a display of the selected alpha-numeric character is provided through the cover.

States Patent [191 Rogers 3,840,770 Oct. 8, 1974 1 GASEOUS DISCHARGEDISPLAY DEVICE WITH EMBEDDED ELECTRODE SEGMENTS [75] Inventor: Bryant C.Rogers, La Jolla, Calif.

[73] Assignee: Diacon, Inc., San Diego, Calif.

[22] Filed: Apr. 4, 1973 [21] Appl. No.: 347,705

[52] US. Cl. 313/517 [51] Int. Cl. H0lj 61/66 [58] Field of Search313/1095, 210, 217

[56] References Cited UNITED STATES PATENTS 3,426,248 3/1966 Cistola315/169 R 3,617,793 11/1971 Matsushita et a1 313/1095 3,735,181 5/1973Kobayakawa et a1 313/1095 3,743,879 7/1973 Kupsky 315/169 TV 3,775,63211/1973 Toda 313/1095 Primary Examiner-Palmer C. Demeo [57] ABSTRACT Agas discharge display device for displaying one of a plurality ofalpha-numeric characters, including a substrate having a glass layerupon its upper surface; a plurality of flat metal segment elementsembedded in the glass layer and arranged laterally in the general shapeof the necessary segments of'all the alphanumeric characters to bedisplayed by the device; a plurality of metal leads, one for eachsegment, each electrically connected to its respective segment andextending outside the periphery of the substrate; a second metal layerelectrically insulated from the segments lying in a plane parallel tothat of the segments and having apertures therein arranged laterally incorrespondence with the segments, the second metal layer beingmechanically supported by the substrate; a metal lead electricallyconnected to the second metal layer also extending outside the peripheryof the substrate; and a cover, at least partially translucent, so

that the segments, when energized, are visible therethrough, the coverenclosing and sealing the segments and the second metal layer, therebyproviding a sealed enclosure with the necessary electrical leads fromthe cathode segments and the anode extending outside the sealedenclosure so that, when the cathode segments are selectivelyelectrically activated, a display of the selected alpha-numericcharacter is provided through the cover.

2 Claims, 3 Drawing Figures amomo PAIENIEBum 81924 FEG.2

1 GASEOUS DISCHARGE DISPLAY DEVICE WITH EMBEDDED ELECTRODE SEGMENTSFIELD OF THE INVENTION This invention is 'in the field of gas dischargedisplay devices. Such display devices are commonly used in the industryfor digital displays and have an anode and a plurality of cathodes whichare selectively energized to cause the gas within the enclosure to glowin a pattern selected by the selective energization of one or aplurality of the cathode elements.

PRIOR ART Gas discharge display devices are well known. For example, US.Pat. No. 3,418,509 shows a device which has the basic configuration ofthe device of the invention. The enclosures of such prior art devicesincludes a substrate, a cap, a plurality of cathode and lead elementcombinations, and a counter electrode or anode which is customarilyformed by a perforated metal layer applied to the inner side of thecover plate. These enclosures of the prior art, however, have beentricky to assemble and test and thus costly to manufacture. Theprincipal reason for this has been the inability to test the deviceuntil it had been totally completed and sealed. At that time, if animproper connection or a lack of a connection was found by testing, theentire unit had to be scrapped. It was impossible to test the unitsuntil the cap, containing the anode layer, was sealed to the base. Atthat stage, unsealing was no longer practical as a means to makerepairs.

Furthermore, in the prior art devices, a complicated sealing procedureis necessitated. The sealing of the package of the prior art, leaving aglass tube extending outside the package for evacuation purposes, iscalled tubulation." The unit is exhausted through a tube and filled withthe desired gas or gas mixture, at which time the tube is closed. Thestub of this tube still extends outside the package after sealing and isan inconvenience in circuit board insertion of the device.

BRIEF DESCRIPTION OF THE INVENTION The gas discharge display device ofthis invention is similar to the packages of the prior art, but has theadvantage that it can be fully assembled and tested prior to attachmentof the cover. In the package of this invention, both the anode elementand the cathode elements are mechanically affixed to the substratebefore the cover is attached. All of the electrical connectionsnecessary to test the unit are thereby completed prior to placing on thecap. After testing, the cap is placed on the unit simultaneously withthe evacuation of the air and the introduction of the necessary gas orgas mixture for the completed device. Any defect in the electricalconnection of the cathode segments or the anode can be corrected priorto scaling and completing the unit. Accordingly, the manufacturingyields of the alpha-numeric character display devices of this inventionare substantially improved.

Briefly, the gas discharge display element of this invention, fordisplaying one of a plurality of alpha numeric characters, includes agas discharge display device for displaying one of a plurality. ofalphanumeric characters including a substrate having a glass layer uponits upper surface; a plurality of flat metal segment elements embeddedin the glass layer and arranged laterally in the general shape of thenecessary segments of all the alpha-numeric characters to be displayedby the device; a plurality of metal leads, one for each segment, eachelectrically connected to its respective segment and extending outsidethe periphery of the substrate; a second metal layer electricallyinsulated from the segments lying in a plane parallel to that of thesegments and having apertures therein arranged laterally incorrespondence with the segments, the second metal layer beingmechanically supported by the substrate; a metal lead electricallyconnected to the second metal layer also extending outside the peripheryof the substrate; and a cover, at least partially translucent, so thatthe segments, when energized, are visible therethrough, the coverenclosing and sealing the segments and the second metal layer, therebyproviding a sealed enclosure with the necessary electrical leads fromthe cathode segments and the anode extending outside the sealedenclosure so that, when the cathode segments are selectivelyelectrically activated, a display of the selected alpha-numericcharacter is provided through the cover.

The device of the invention is sealed by attaching the cover in anevacuated atmosphere into which the desired gas or-gas mixture isintroduced. No tubulation process or tube extending outside the packageis required.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional drawing of thegasdischarge display device of the invention;

FIG. 2 is a top view of the substrate of this invention showing thecathode segments, the cathode connecting I DETAILED DESCRIPTION OF THEINVENTION Referring to the drawings, particularly to FIG. 1, the basicparts of the gas discharge display device of the invention all are.formed on substrate 10. Substrate 10 conventionally is ceramic. However,metal or other conductive materials could be used since the glass layer11 provides the necessary insulation between the substrate 10 and theconductive cathode and lead elements, 12, 20, 21 and 22. In theembodiment shown in the drawings, for example, the cathode is comprisedof seven character display elements 20, along with a decimal pointelement 21. Cathode elements 20, shown in FIG. 2, are arranged in thesegments of a FIG. 8". As is well known in the art, with a 7-segmentFIG. 8, the selective activation of two or more cathode elements issufficient to display all of the digits 0 through 9. Element 21 is usedto display the decimal point. The segment arrangement is conventional inthe art and needs no further explanation here.

Referring to FIG. 2, the plurality of substantially flat metal segments20, making up the cathodes, are embedded in glass layers 11 and 24 (onlylower layer 11 being shown in FIG. 2) but are exposed and free fromglass on their upper surfaces 30 shown in FIG. 1. The leads 22 and 25,shown in FIG. 2 are connected'to' the respective cathode elements andanode contact 26 and are normally embedded in the glass layers 11 and 24as shown in FIG. 1, to hold them tightly on the substrate. The glasslayers 11 and 24 also insulate the metal cathode elements at portions oftheir surface which otherlead prior to deposiwise might causeundesirable sputtering during device operation and thus decrease theuseful life of the final device. These metal leads, one for each cathodesegment 20 and 21 and one for anode contact 26 are electricallyconnected to the respective segment or contact as shown in FIG. 2, andextend at least beyond the periphery of substrate 10. For convenience ofmanufacture, all of the leads 22 and cathode elements 20 and 21 as wellas lead 25 connected to anode terminal 26 can be stamped or etchedsimultaneously in a frame pattern held together by bars 23. Bars 23 areremoved after the leads have been mechanically attached to the substrateby the glass so that the individual parts 21, 22, and 26 are separatelyavailable for electrical testing.

The fabrication of the substrate of the invention begins by assemblingthe cathode elements, leads, contact and frame assembly 20, 21, 22, 23,25, and 26 onto the substrate. Referring to FIG. 1, first a layer of aslurry of devitrifiable glass material 11 is deposited upon thesubstrate over the entire substrate. A devitrifiable glass is a type ofglass which is capable of being devitri fied. Devitrification is thegrowth of crystalline material in the glass. In normal glass-makingprocedures, steps are taken to prevent devitrification. However, inconnection with the encapsulation of the devices of the invention, aseal is made by employing a deliberate devitrification step. Thecomposition of the glass material 11 can be one of many glasses capableof devitrification. Representative compositions are described in U.S.Pat. No. 3,248,350. These devitrifiable glass compositions aredevitrified at temperatures normally in excess of 400C, as described inthat patent.

The layer 11 of sealing glass is initially applied at a relatively lowtemperature, and subsequently converted by devitrification at a highertemperature to a material of crystalline character that will withstandsubsequent high temperature environments without softening of flowing.

The lead frame assembly 20, 21, 22, 23, 25, and 26 is placed onto theglass layer 11. The assembly, including substrate 10, glass layer 11,cathodes 20, 21, leads 22 and 25, frame 23 and contact 26 with theleads, cathode elements, and contact resting in the glass, is placedinto a conventional devitrification furnace. Devitrification can becarried out at temperatures ranging from 450C to 550C at times between 2minutes and I hour. Using, for example, a glass composition calledCV-98" sold by Owens-Illinois, devitrification takes placesatisfactorily at 500C in about 5 minutes. After devitrification, theassembly including cathode elements and 21, and leads 22 and (FIG. 2)and contact 26 are embedded in layer 11, leaving only cathode elements20 and 21 and contact 26 free of glass.

After the assembly has been removed from the devitrification oven andcooled, a second glass layer 24 shown in FIG. 1 can be applied. Thesecond layer 24 is also devitrifiable glass material, and must havethermal expansion characteristics compatible with the substrate, theprevious glass layer and the metal lead frame. However, it is notnecessary that it be the identical glass layer as the first layer aslong as the above criteria are met. The second layer is laid down on topof the first devitrified layer, covering the leads 22 and 25 (FIG. 2)but not the cathode elements 20 and 21 or contact 26. Leads 22 and 25extend beyond the glass layer and beyond to the perimeter of substrate10. It is important that the cathode elements 20 and 21 remain free ofglass or else they will not glow when activated. It is equallyimportant, however, that the corners of the metal be covered to preventsputtering, as discussed above. Contact 26 must be free of glass so theanode may be electrically connected. The second glass layer 24 isdeposited at temperatures and times which will not permitdevitrification. The layer is, however, preferably sintered attemperatures ranging from about 425C to 480C, these temperatures beingselected to be below the devitrification conditions (time andtemperature) of the glass composition employed. The purpose of thesintering step is merely to solidify the glass layer, but to leave itnon-devitrified so it can be later devitrified in the final sealing ofthe cap to the package.

Included in the lead configuration shown in FIG. 2 are one or more anodeleads 25, connected to an anode contact 26. Anode contact 26 is to beconnected to tab 27 (shown in FIGS. 1 and 3), preferably formed as anintegral part of anode element 14, shown in FIG. 1. The anode contact 26and tab 27 together serve to rigidly hold the anode 14 onto thesubstrate 10 as shown in FIG. 1. Anode contact 26 must make electricalcontact with the anode element 14 through tab 27. Tab 27 also holds theanode element 14 separated from the cathode segments 20 and 21 and theirassociated leads 22. For structural rigidity, additional mechanicalseparating supports or tabs 28 can be provided integral with orconnected to anode element 14, but which need not necessarily also makeelectrical contact to anode lead 25. One electrical connection is allthat is required.

As shown in FIG. 3, anode element 14 has apertures 29 and 31 which arearranged laterally in correspondence with the plurality of cathodesegments 20 and 21 shown in FIG. 2 in the final assembly. The anodeelement 14 is stamped from a suitable sheet metal such as stainlesssteel. During the stamping, at least two opposing sides of the aperture,preferably the major or longer sides, are drawn to an angle of at least45, preferably approximately to the planar viewing surface, resulting inthe drawn lips 15 shown in FIG. 1. The apertures 29 and 31, shown inFIG. 3 are punched outwith the drawn lips 15, shown in FIG. 1, lying onthe side of the anode layer facing the exposed cathode elements atapertures 30. These lips 15, extending below the plane of anode 14, asshown in FIG. 1, act as illumination multipliers by reflecting the gasdischarge image of the cathode elements 20 and 21 (FIG. 2). This effectprovides a brighter image outline compared to the systems of the priorart where the outline of the image is of lower density than the centralarea of the design. Drawn lips 15 of anode 14 insure that the imagedensity of the outline isat least as bright as the image density of thecentral area.

By virtue of drawn lips 15 extending below the main plane of the anodelayer 14, down to the immediate region of the cathode elements 20 and21, the device achieves an improved field focusing of the cathodeanodevoltage. Furthermore, the cross-talk associated with conventional gasdischarge devices is reduced and the ratio of the desired image to theimage cross-talk is increased in the display device of the invention.

Anode layer 14 is rigidly attached, such as by brazing or soldering, toanode contact 26. Alternatively, layer 14 and contact 26 may be formedintegrally, such as by stamping the portion 26 being embedded in glasslayer 24. This feature elminates the prior art ohmic spring typecontacts which were considered necessary to electrically connect thetransparent conductive coatings which were formed under the covers ofthe devices. Extra supports 28 are placed to rest at the same time onglass layer 11, as shown in FIG. 1, prior to the attachment of cap 17.The preassembly of the anode and the cathode elements of the subjectinvention permits adjustment in the alignment of the cathode and anodeor in the spacing between them to achieve optimum operatingcharacteristics prior to final assembly and attachment of the cap. I

Finally, after any adjustments, testing, and alignment is completed, cap17 is attached to the glass layer 24. Referring to FIG. 1, preferablythe bottom portion of cap 17, adjacent to glass layer 24, is glass-free.In the sealing technique of this invention, the cap 17 is heated to atemperature greater than the softening point of glass layer 24 onsubstrate 10. Preferably the cap 17 is held in the heater block of aconventional assembly jig. The entire heater block and assembly jig areplaced in a conventional evacuated chamber during the sealing process.If desired, substrate can also be heated using an additional heatingblock beneath the substrate. The substrate is heated sufficiently sothat the glass layer 11 and 24 reach an elevated temperature below theirsoftening point. if the glass layers were heated to a temperature at orabove their softening point, the cathode and lead elements may tend toshift, and premature devitrification of the sealing glass may occurwhich would cause unreliable sealing. Accordingly, it is essential thatthe glass layers 11 and 24 remain at a temperature below their softeningpoint up to the time when they are contacted by the heated cap 17.

After the heating of the parts has been completed in the vacuum chamber,the vacuum is replaced by the desired gas or gas mixture to be enclosedin the device. These gases are conventional in the art. During thesealing step, the entire atmosphere around the device will be the gasdesired to be introduced into the package after final sealing. Once thegas has equilibrated in the chamber, the cap 17 is contacted with theglass layer 24 on substrate 10. This may be accomplished by lowering thecap into position or raising the substrate while the cap remains in itsheater block. The heat conducted from the heater block adjacent the capduring sealing processes passes through the cap 17 and serves to softenthe glass layer 24, thereby effecting a seal between the two parts ofthe package upon contact.

After'the sealing operation has been completed, the vacuum and gasatmosphere in the chamber may be released, and the device removed fromthe chamber.

The above sealing operation completely avoids the tubulation proceduresrequired in the prior art, wherein a tube extends from the package aftersealing and is subsequently used for the introduction of the proper gasinto the chamber. By elimination of'this tubulation process, the userwill not be hampered by the existence of a tube extending from thebottom side of the package which gets in the way during the assembly ofthe package onto a conventional printed circuit board.

I claim:

1. A gas discharge display device for displaying one of a plurality ofalpha-numeric characters comprising:

a substrate having a glass layer on its upper surface;

a plurality of substantially flat metal segments embedded in said glasslayer and arranged laterally in the general shape of the necessarysegments of all of the alpha-numeric characters to be displayed by saiddevice;

a plurality of metal leads, one for each segment, each electricallyconnected to its respective segment and extending outside the peripheryof said substrate;

a second metal layer lying in a plane parallel to the plane of saidsegments and electrically insulated from said segments, said secondmetal layer having apertures therein arranged laterally incorrespondence with said segments, said second metal layer beingmechanically supported by said glass layer and said substrate, at leastthe major edges of the apertures of said second metal layer beinginwardly bent on an angle exceeding 45 with the main plane of saidsecond metal layer;

a metal lead electrically connected to said second metal layer and alsoextending outside the periphery of said substrate; and

a cover, at least partially translucent so that said segments, whenenergized, are visible therethrough. said cover enclosing and sealingsaid segments and said second metal layer, thereby providing a sealedgaseous atmosphere in the enclosure with the necessary electrical leadsextending outside of said sealed enclosure which, when said leads areselectively electrically activated, provide a display of the selectedalpha-numeric character through said cover.

2. The gas discharge display device of claim 1 further characterized bysaid angle being approximately

1. A gas discharge display device for displaying one of a plurality ofalpha-numeric characters comprising: a substrate having a glass layer onits upper surface; a plurality of substantially flat metal segmentsembedded in said glass layer and arranged laterally in the general shapeof the necessary segments of all of the alpha-numeric characters to bedisplayed by said device; a plurality of metal leads, one for eachsegment, each electrically connected to its respective segment andextending outside the periphery of said substrate; a second metal layerlying in a plane parallel to the plane of said segments and electricallyinsulated from said segments, said second metal layer having aperturestherein arranged laterally in correspondence with said segments, saidsecond metal layer being mechanically supported by said glass layer andsaid substrate, at least the major edges of the apertures of said secondmetal layer being inwardly bent an an angle exceediNg 45* with the mainplane of said second metal layer; a metal lead electrically connected tosaid second metal layer and also extending outside the periphery of saidsubstrate; and a cover, at least partially translucent so that saidsegments, when energized, are visible therethrough, said cover enclosingand sealing said segments and said second metal layer, thereby providinga sealed gaseous atmosphere in the enclosure with the necessaryelectrical leads extending outside of said sealed enclosure which, whensaid leads are selectively electrically activated, provide a display ofthe selected alpha-numeric character through said cover.
 2. The gasdischarge display device of claim 1 further characterized by said anglebeing approximately 90*.